1. Field of the Invention
The present invention relates in general to a dressing apparatus and relates in particular to a dressing apparatus used in conjunction with a polishing apparatus for producing a flat mirror polished surface on semiconductor wafers.
2. Description of the Related Art
High density integrated semiconductor devices of recent years require increasingly finer microcircuits, and the interline spacing has also shown a steadily decreasing trend. For optical lithography operations based on less than 0.5 micrometer interline spacing, the depth of focus is shallow and high precision in flatness is required on the polishing object which has to be coincident with the focusing plane of the stepper. This requirement means that the wafer surface must be made extremely flat, and a first step in achieving such precision in flatness begins with proper surface preparation by polishing with a polishing apparatus.
The conventional type of polishing apparatus used in such applications comprises a turntable with a polishing cloth mounted on a top surface, a topring, each of which having independent rotational control, and a polishing object disposed therebetween. The surface of the object to be polished is pressed down onto the polishing cloth by the topring exerting a controlled pressure while spraying an abrasive liquid on the polishing cloth from an abrasive liquid nozzle. The polishing process is continued until the polishing surface is polished to the required degree of flatness and mirror polish.
In such a polishing apparatus, the polishing cloth mounted on top of the turntable becomes clogged with particles of polishing powder which may adhere to or penetrate the polishing cloth. For this reason, the polishing cloth must be resurfaced from time to time by removing the particles and dressing the cloth. Therefore, it is necessary that a polishing apparatus be provided with a dressing facility.
FIG. 4A is a side view of a conventional dressing device and FIG. 4B is a plan view of the dressing device shown in FIG. 4A. The dressing device has a brush 32 attached to an arm 31. To perform dressing on the polishing cloth 34 mounted on the turntable 33, the turntable 33 is revolved while the tip of the brush 32 touching the polishing cloth 34 and washing solution W such as deionized water is being sprayed through a nozzle 35.
The conventional dressing device of the type shown in FIG. 4A and 4B presents some operational problems that it is difficult to wash the entire surface of the polishing cloth 34 uniformly and thoroughly, and to remove the particles adequately which become lodged in the cloth. Therefore, the serviceable life of the polishing cloth 34 is short, and the polishing cloth 34 needs to be changed frequently.
To resolve such difficulties, a dressing device shown in FIG. 5A showing a side view has been disclosed in a Japanese Laid-open Patent Publication, H6-190714. This dressing device comprises: an arm 42 for holding a revolving brush 41; and a swing device 43 for providing a swinging action for the arm 42. There is a driving source (electrical motor) 44 provided at the proximal end of the arm 42 for revolving the brush 41. The brush 41 is revolved by the driving source 44 through a force transmission device, such as a pulley belt 45, disposed inside the arm 42, and can be moved up or down by moving a support post 46 for the arm 42 so as to apply some pressure on the polishing cloth 48.
However, the dressing device described above present the following operational problems.
First, it is important that the brush be pressed against the cloth with a certain pressure. However, the construction of the dressing device is such that the brush is located at the end of a long arm, and the rigidity of the arm is insufficient to provide the required pressure because of flexing of the arm. It is also difficult to apply uniform pressure on the cloth through the brush, resulting in non-uniform dressing of the polishing cloth.
If the arm is stiffened in an effort to apply sufficient pressure on the cloth, the weight of device becomes heavy and the design of the device becomes complex.
Furthermore, in the conventional dressing device since the driving force must be transmitted through a long distance in the arm, the transmission mechanism becomes complex and requires a high maintenance work.